The present invention concerns a new phosphatidyl-inositol-3-kinase (PI3K.gamma.), a nucleic acid which codes for it, an antibody directed against the protein as well as the diagnostic and therapeutic use of the protein, of the nucleic acid and of the antibody.
Phosphatidylinositol-kinases belong, together with specific phospholipases, to an enzyme group which catalyses the formation of intracellular messenger substances from the membrane lipid phosphatidyl inositol (PI). The activity of these enzymes is regulated by extracellular effectors such as hormones, growth factors and neurotransmitters. It is assumed that the PI dependent messenger substances are involved among other processes in the regulation of important cells functions such as cell proliferation, secretion of cellular constituents, endocytotic processes, the targetted movement of certain cells, controlled changes of the cytoskeleton. Correspondingly the physiological importance of the PI kinases and phospholipases correlates with a series of disease states involving changes of the functions of these enzymes.
From various experimental results it is possible to conclude that the product of the reaction catalysed by PI3 kinase, PI-3,4,5 triphosphate plays an important role in the regulation of the following physiological cell functions:
Regulation of cell proliferation and cell differentiation by PI 3 kinase
Mitogens such as growth factors and cytokines generally lead to a stimulation of the PI 3 kinase activity in cells capable of division. The oncogenic transformation of cells is also often accompanied by an increase in the measurable PI 3 kinase activity (Varticovski et al., Biochim. Biophys. Acta 1226, 1-11 (1994), Berggren et al., Cancer Research 53, 4297-4302 (1993), Soldi et al., Oncogene 9, 2253-2260 (1994)). Inhibitors of PI 3 kinase are able to inhibit the PDGF-stimulated growth of normal connective tissue cells or smooth muscle cells and the proliferation of src-supratransformed fibroblasts (cancer cells) (Berggren et al., Cancer Research 53, 4297-4302 (1993), Vlahos et al., J.Biol.Chem. 269, 5241-5248 (1994)). Berggren et al., have speculated that the tumoristatic effect of ether lipid analogues is mainly based on their inhibitory action on PI 3 kinase.
The differentiation of the nerve cell line PC12 is suppressed by wortmannin an inhibitor of PI 3 kinase (Kimurea et al., J.Biol.Chem. 269, 18961-18967 (1994)). These findings as well as a clinical study in which there was shown to be a selective loss of PI 3 kinase activity in the brain of Alzheimer patients (Bothmer et al., Dementia 5, 6-11 (1994)) indicate that the enzyme has an important function in the formation and maintenance of nerve tissue.
Regulation of cytoskeletal-dependent processes by PI 3 kinase
Microscopically visible changes of cells often progress with the involvement of the cytoskeleton. A series of results shows that at least some of these processes are regulated by PI 3 kinase and its enzymatic products (PI3,4,5,P.sub.3, PI3,4P.sub.2 and PI3P). Thus the membrane ruffling of epidermal cells induced by insulin or PDGF can be suppressed by the PI 3 kinase inhibitor wortmannin (Kotani et al., EMBO J. 13, 2313-2321 (1994), Wennstrom et al., Curr. Biol. 4, 385-393 (1994)).
Basophilic leucocytes are able to secrete histamine--a mediator of inflammations and allergic symptoms. The cytoskeleton of the cells is involved in this secretion process. Yano et al., J. Biol.Chem. 268, 25846-25856 (1993) were able to show that the antibody-induced histamine secretion can in turn be inhibited by the PI 3 kinase inhibitor wortmannin i.e. it is apparently controlled by 3-phosphorylated phosphoinositides.
Involvement of PI 3 kinase in intracellular transport processes
Investigations on yeast mutants show that one form of PI 3 kinase (Vps 34) is involved in these organisms in the selective distribution of proteins towards the yeast vacuoles (Schu et al., Science 260, 88-91 (1993)). Similar mechanisms may be the basis of the insulin-stimulated translocation of glucose transport protein (GLUT 4) from the interior of the cell to the plasma membrane (Kanai et al., Biochem.Biophys.Res.Commun. 195, 762-768 (1993)). This important process in various organs is also inhibited by wortmannin and apparently involves PI 3 kinase.
Inhibition of the O.sub.2.sup.- production in neutrophilic granulocytes
Granulocytes produce superoxide anions (O.sub.2.sup.- ) with the aim of destroying phagocytised foreign cells. This process is stimulated by the chemoattractant fMLP. The blocking of the fMLP-induced O.sub.2.sup.- formation by wortmannin indicates a regulatory function of a PI 3 kinase species in this important process for the immune response of the body.
The above-mentioned results underlin e the central importance of PI 3 kinase and 3-phosphorylated inositol lipids in the regulation of important cell functions. Acquired or inherited defects of the said cell functions are undoubtedly the underlying cause of important clinical syndromes. Examples are: cancer, arteriosclerosis, immunopathies, skin diseases (such as psoriasis), degenerative diseases of the nervous system.
Since Pi 3 kinase is an essential element in the regulation of the said cell functions it is very probable that some of the clinical syndromes are due to malfunctions of PI 3 kinase species. The clinical study on PI 3 kinase in the brain of Alzheimer patients, the findings on the role of PI 3 kinase in the formation of the allergy inducer histamine and also the cancerostatic effect of PI 3 kinase-inhibiting ether lipids point in this direction.
A central concern of cell biology is to discover the mechanisms of intracellular signal transmission and the messenger substances that are involved. The final goal of these investigations is to selectively influence cell functions in a medical sense.